DS1has become an industry standard for telecommunication data format. In standard DS1, voice signals are digitalized at 64 kilobits per second (Kb/s), and 24 such 64 Kb/s streams are multiplexed into a 1.544 megabits per second (Mb/s) DS1 signal and transmitted over a T1 trunk. Often a 56 Kb/s or 64 Kb/s digital data signal is substituted for a digitalized voice signal. A waveform encoding technique, commonly referred to as ADPCM (adaptive differential pulse code modulation), compresses voice data to 32 Kb/s and allows a T1 trunk to carry up to 48 voice channels. However, because certain digital data signals of 56 Kb/s or 64 Kb/s are not compressible, the effective compression ratio over standard DS1 is less than 2:1. Standard ADPCM also cannot support voice-band-modem calls where the baud rate is 9.6 Kb/s or higher.
Recently, other waveform encoding techniques have been developed that encode voice data in 16 Kb/s or 24 Kb/s. In using these techniques, greater than 2:1 compression ratio is achieved, but at the cost of poorer data quality.
Another type of data compression technique is digital speech interpolation or DSI. The underlying idea of DSI is to use characteristics of human conversation. In a typical telephone conversation between two parties or more, usually only one party is talking at any one time. In other words, the transmission may be unidirectional most of the time. Additionally, human speech pattern usually includes periods of silence, where transmission is not required. Accordingly, DSI enables a reduction of transmission data by utilizing the statistical nature of human speech and conversation.
It is desirable to compress data at a ratio of greater than 2:1 without compromising the quality of data. It is further desirable to carry modem communication data signals of 56 Kb/s and 64 Kb/s. This is accomplished in the present invention by combining waveform encoding technology with DSI, in which data is packed into packets for transmission.
Accordingly, the present invention provides for packing compressed data from four DS1 trunks into the space of one DS1 trunk. The present invention further provides for unpacking the data in a packed DS1 trunk into four DS1 trunks. Moreover, the present invention is directed to overcoming one or more of the problems as set forth above.